3131 results

  • A first collective validation of global fluvial flood models for major floods in Nigeria and Mozambique

    Authors: Bernhofen, M.V.; Winsemius, H.C. (2018)
    Published in: Environmental research letters (2018), page 1-18

    Global flood models (GFMs) are becoming increasingly important for disaster risk management internationally. However, these models have had little validation against observed flood events, making it difficult to compare model performance. In this paper, we introduce the first collective validation of multiple GFMs against the same events and we analyze how different model structures influence performance. We identify three hydraulically diverse regions in Africa with recent large scale flood events: Lokoja, Nigeria; Idah, Nigeria; and Chemba, Mozambique.We then evaluate the flood extent output provided by six GFMs against satellite observations of historical flood extents in these regions. The Critical Success Index of individual models across the three regions ranges from 0.45 to 0.7 and the percentage of flood captured ranges from 52% to 97%. Site specific conditions influence performance as the models score better in the confined floodplain of Lokoja but score poorly in Idah’s flat extensive floodplain. 2D hydrodynamic models are shown to perform favourably. The models forced by gauged flow data show a greater level of return period accuracy compared to those forced by climate reanalysis data. Using the results of our analysis, we create and validate a three-model ensemble to investigate the usefulness of ensemble modelling in a flood hazard context. We find the ensemble model performs similarly to the best individual and aggregated models. In the three study regions, we found no correlation between performance and the spatial resolution of the models. The best individual models show an acceptable level of performance for these large rivers.

  • Benchmarking flexible meshes and regular grids for large-scale fluvial inundation modelling

    Authors: Hoch, J.M.; Beek, R. van; Winsemius, H.C.; Bierkens, M.F.P. (2018)
    Published in: Advances in water resources (2018), page 1-20

    Damage resulting from flood events is increasing world-wide, requiring the implementation of mitigation and adaption measures. To facilitate their implementation, it is essential to correctly model flood hazard at the large scale, yet fine spatial resolution. To reduce the computational load of models, flexible meshes are an efficient means compared to uniform regular grids. Yet, thus far they have been applied only for bespoke small-scale studies requiring a high level of a priori grid preparation. To better understand possible advantages as well as shortcomings of their application for large-scale riverine inundation simulations, three different flexible meshes were derived from Height Above Nearest Drainage (HAND) data and compared with regular grids under identical spatially explicit hydrologic forcing by using GLOFRIM, a framework for integrated hydrologic-hydrodynamic inundation modelling. By means of GLOFRIM, output from the global hydrologic model PCR-GLOBWB was passed to the hydrodynamic model Delft3D Flexible Mesh. Results show that applying flexible meshes can be beneficial depending on the envisaged purpose. For discharge simulations, similar model accuracy was obtained between flexible and regular grids, with the former generally having shorter run times. For inundation extent simulations, however, the coarser gridding of flexible meshes in upstream areas results in a poorer performance if assessed by contingency maps. Moreover, while the ratio between minimum and maximum spatial resolution of flexible meshes has limited impact on discharge simulations, water level estimates may be stronger influenced by the application of larger grid cells. . As this study presents only a small set of possible realizations, additional research needs to unravel how the data and methods used as well as the choices for discretizations influence model performance. Generally, the application and particularly discretization process of flexible meshes involves more options, bringing more responsibilities for the user. Once an a priori decision is made on the model purpose, flexible meshes can be a valuable addition to modelling approaches where short run times are essential, facilitating large-scale flood simulations, ensemble modelling or operational flood forecasting.

  • Development of an Integrated Biophysical Model to represent morphological and ecological processes in a changing deltaic and coastal ecosystem

    Authors: Baustian, M.M.; Maren, D.S. van; Jeuken, M. (2018)
    Published in: Environmental modelling and software, volume 109 (2018), page 402-419

    Deltaic and coastal ecosystems are changing in response to natural and anthropogenic forces that require ecosystem-level restoration efforts to avoid habitat degradation or loss. Models that link ecosystem components of hydrodynamics, morphodynamics, nutrient and vegetation dynamics to represent essential processes and feedbacks are advancing the field of environmental modeling and are vital to inform coastal restoration decisions. An Integrated Biophysical Model was developed by creating a new vegetation dynamics component and linking it to other primary ecosystem components that included essential feedbacks. The model performance was evaluated by applying it to a deltaic ecosystem that included marshes and estuaries. The Integrated Biophysical Model output captured the general temporal and spatial environmental trends of key variables. This integrated model is capable to perform long-term simulations to assess responses of deltaic and coastal systems to global change scenarios and can be used to inform restoration strategies in ecosystems worldwide.

  • Internal erosion in earthdams, dikes and levees : proceedings of EWG-IE 26th annual meeting (Milano, Italy, September 10 to 13,2018)

    Authors: Bonelli, S.; Jommi, C.; Sterpi, D.; European Working Group on Internal Erosion (2018)

  • Scenariostudie natuurperspectief Grevelingenmeer

    Authors: Tangelder, M.; Wijsman, J.; Janssen, J.; Nolte, A.J.; Walles, B.; Ysebaert, T. (2018)

    In de Rijksstructuurvisie (RSV) Grevelingen en Volkerak-Zoommeer zijn diverse oplossingsrichtingen verkend om de waterkwaliteit te verbeteren als voorbereiding op een Rijksbesluit. In de planvorming is voor het Grevelingenmeer gekeken naar kansen vanuit verschillende invalshoeken zoals waterkwaliteit, getijdenenergie en waterveiligheid. Natuurorganisaties waren van mening dat hierbij vooral aandacht is geweest voor effecten op huidige beschermde natuurwaarden (in relatie tot Natura 2000-wetgeving), maar dat er slechts beperkte aandacht is geweest voor kansen voor het verzilveren van nieuwe (estuariene) natuurwaarden en optimalisatie mogelijkheden van toekomstig waterbeheer ten bate van natuurwaarden in een situatie met gedempt getij. Het ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV) vindt het van belang dat het perspectief en de kansen voor natuur in het Grevelingenmeer grondiger worden uitgediept met betrokkenheid van verschillende experts en dat natuurpartijen (lokaal en landelijk), beheerders (Staatsbosbeheer en RWS) en provincies hierbij worden betrokken. Daarom heeft zij Wageningen Marine Research gevraagd om dit nader te onderzoeken. Er is aangesloten op het voorkeursalternatief van de RSV (50 cm getij), maar daarnaast zijn ook breder de gevolgen voor de natuur van (1) een kleinere getijslag en (2) een aangepast peilbeheer onderzocht en er is een doorkijk gegeven naar de lange termijn gevolgen waarbij tevens het effect van zeespiegelstijging is meegenomen.

  • Influence of El Niño Southern Oscillation on global coastal flooding

    Authors: Muis, S.; Haigh, I.D.; Guimaraes Nobre, G.; Aerts, J.C.J.H.; Ward, P.J. (2018)
    Published in: Earth's future : an open access AGU journal (2018), page 1-19

    Anomalous atmosphere-ocean conditions in the tropical Pacific associated with the El Niño Southern Oscillation (ENSO) drive interannual variations in mean and extreme sea levels. Climate change may lead to more frequent extreme ENSO events in the future. Therefore, it is important to enhance our understanding of ENSO's influence on coastal flood impacts. We assessed ENSO’s influence on extreme sea levels using a global reanalysis of tides and storm surges. This allows for a full coverage of the global coastline from 1979 to 2014. A mean sea level component is added to account for steric effects. This results in a substantial improvement in the representation of the seasonal and interannual variability. Our results show significant correlations across the Pacific between ENSO and extreme sea levels (expressed as 95th annual percentiles), which is consistent with previous studies based on tide gauge observations. Average anomalies in the annual percentiles over El Niño years compared to neutral years show similar patterns. When examining total sea levels, results are largely statistically insignificant. This is because in many regions large tidal variability dominates over the other components. Combining sea levels with an inundation and impact model shows that ENSO has a significant but small effect on the number of people potentially exposed to flooding at the globally aggregated-scale. Our result demonstrate that a model-based approach allows for an assessment of the influence of ENSO on coastal flood impacts, and could be used to assess impacts of future changes in ENSO.

  • Global modeling of tropical cyclone storm surges using high-resolution forecasts

    Authors: Bloemendaal, N.; Muis, S.; Haarsma, R.J.; Verlaan, M.; Irazoqui Apecechea, M.; Moel, H. de; Ward, P.J.; Aerts, J.C.J.H. (2018)
    Published in: Climate Dynamics (2018), page 1-14

    We assess the suitability of ECMWF Integrated Forecasting System (IFS) data for the global modeling of tropical cyclone (TC) storm surges. We extract meteorological forcing from the IFS at a 0.225° horizontal resolution for eight historical TCs and simulate the corresponding surges using the global tide and surge model. Maximum surge heights for Hurricanes Irma and Sandy are compared with tide gauge observations, with R2-values of 0.86 and 0.74 respectively. Maximum surge heights for the other TCs are in line with literature. Our case studies demonstrate that a horizontal resolution of 0.225° is sufficient for the large-scale modeling of TC surges. By upscaling the meteorological forcing to coarser resolutions as low as 1.0°, we assess the effects of horizontal resolution on the performance of surge modeling. We demonstrate that coarser resolutions result in lower-modeled surges for all case studies, with modeled surges up to 1 m lower for Irma and Nargis. The largest differences in surges between the different resolutions are found for the TCs with the highest surges. We discuss possible drivers of maximum surge heights (TC size, intensity, and coastal slope and complexity), and find that coastal complexity and slope play a more profound role than TC size and intensity alone. The highest surges are found in areas with complex coastlines (fractal dimension > 1.10) and, in general, shallow coastlines. Our findings show that using high-resolution meteorological forcing is particularly beneficial for areas prone to high TC surges, since these surges are reduced the most in coarse-resolution datasets.

  • Validatie van Steentoets 2010 : stabiliteit van steenzettingen

    Authors: Klein Breteler, M.A.; Mourik, G.C. (2012)

    In het kader van de toetsing van de waterkeringen zoals voorgeschreven in de Waterwet dienen ook steenzettingen elke zes jaar getoetst te worden. Volgens de VTV2006 moet dit uitgevoerd worden met het Excel-programma Steentoets (Klein Breteler, 2011). Daarnaast kan Steentoets gebruikt worden als hulpmiddel voor het ontwerpen van steenzettingen. Het programma is ten behoeve van de toepassing in de derde toetsronde uitgebreid gevalideerd aan de hand van Deltagootproeven en er is een analyse uitgevoerd van de trends in de resultaten als parameters worden gewijzigd (Klein Breteler, 2009). De toenmalige versie van Steentoets betrof Steentoets2008, versie 0.80. Sindsdien is de kennisontwikkeling op het gebied van de stabiliteit van steenzettingen verdergegaan. Deze nieuwe ontwikkelingen hebben geleid tot verbeteringen in het rekenmodel. Om te kunnen beoordelen of deze ontwikkelingen nog steeds in lijn zijn met de beschikbare resultaten van grootschalig modelonderzoek is in deze rapportage opnieuw een vergelijking gemaakt tussen de resultaten van Steentoets en de beschikbare grootschalige modelproeven. Daar is nu Steentoets2010, versie 1.09, voor gebruikt. Tevens zijn de trends weer geanalyseerd en is beoordeeld of deze realistisch zijn.

  • Rapportage geologisch onderzoek zoekgebieden Noordzee zandwinning

    Authors: Blauw, M.; Kleine, M.P.E. de; Vonhögen-Peeters, L.M.; Heteren, S. van; Weert, J.P.A. de; Gaans, P.F.M. van (2017)

    In 2016, is in opdracht van RWS Kustlijnzorg en Stichting LaMER, een grootschalige geologisch onderzoek uitgevoerd voor het vaststellen van de geologische opbouw van 105 potentiële zoekgebieden voor de winning van suppletie- en ophoogzand. Het doel van het geologisch onderzoek was om inzicht te krijgen 1) in het voorkomen van stoorlagen die de effectieve winbaarheid van het zand in de weg staan en 2) in de kwaliteit van het beschikbare zand. Daarnaast is gekeken naar de aanwezige slibconcentraties in de ondergrond, ten behoeve van het modellenonderzoek naar de ecologische effecten van een toename van de slibconcentraties in de Noordzee als gevolg van zandwinning. Het voorliggende onderzoek is onderdeel van het MEP 2014-2017 en vormt daarmee input voor het MER 2018-2027. De zoekgebieden worden definitief vastgesteld in het MER en vormen de basis voor de ontgrondingsvergunningen voor de komende 10 jaar.

  • R&D highlights Deltares edition 2018

    Authors: Kruiver, P.P.; Stuparu, D. (2018)

    Deltares aims to make the research and development results (R&D) more accessible to the public and the private sector. The chapters in this 2018 report follow the structure of the six issues that are central to the Deltares mission: Enabling technologies; Delta infrastructure; Water and subsoil resources; Adaptive delta planning; Ecosystems and environmental quality; Flood risk.

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